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6 Conclusion

This work undertaken directly in the wake of the Hipparcos Catalogue publication is probably not the ultimate, although we have gone through the Hipparcos data bases in a very systematic way. We think that we have done outside the rigourous time constraint of the project what could be achieved without departing too much from the standard models used in the mass processing.

However it remains a significant number of well observed targets with poor solutions, or no solution at all, for which no satisfactory explanation has been given so far. It is very likely that they belong to three main sources: (i) the target pointed is at more that 20 arcsec from an actual star, and in this case there is virtually no hope to retrieve any valuable science information; (ii) the star observed is in fact a double system with an orbital period between 1 and 10 years and a full solution cannot be obtained without additional input data and extensive software development, for example to split the observation period in two or three sub-intervals; (iii) the target is a multiple system with weak hierachy, involving at the same time a very complex model and too many unknown parameters for a reliable solution to be concluded from the Hipparcos observations alone. The publication of the intermediate data and that of the calibrated signal parameters provided on the Catalogue CD-ROMs is the basic material from which any new investigation should start to solve these very troublesome cases.

Finally after the examination of nearly a thousand systems, we are still left with more than two hundreds suspected non single stars, now confirmed at least double in the images of the Digitized Sky Survey, but which did not yield an acceptable solution with the Hipparcos raw data. As most of these stars are new binaries, this list is of interest for double star observers and it will be put into a convenient format and posted on the Hipparcos website.

Acknowledgements

The Digitized Sky Surveys were produced at the Space Telescope Science Institute under U.S. Government grant NAG W-2166. The images of these surveys are based on photographic data obtained using the Oschin Schmidt Telescope on Palomar Mountain and the UK Schmidt Telescope. The California Institute of Technology, the National Geographic Society, the National Science Foundation, the Sloan Foundation, the Samuel Oschin Foundation, the Eastman Kodak Corporation, the UK PPARC and the Royal Observatory of Edinburgh are gratefully acknowledged for their invaluable contribution.

P. Lampens, J. Cuypers, W. Seggewiss and E. Oblak are gratefully acknowledged for a pre-publication release of new observational double star data. Constructive remarks and suggestions from M. Perryman were useful and appreciated.


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